Drag reduction mechanism of the 3D geometry of foreleg's claw toe of the mole cricket (Gryllotalpa orientalis)

Biological plane geometry has been unable to meet the harsh requirements of bionic design in most soil contacting parts of tillage machinery in recent years, particularly on the operating speed, energy-saving, and emission reduction. In this study, a bionic investigation was performed on the toe of the foreleg claw in the mole cricket using the three-dimensional (3D) geometry. Projection and segmentation were also used to extract the 3D characteristic curves of claw toe in three orthogonal planes. The MATLAB platform was selected to determine the characteristic curves via the polynomial fitting and smoothing processing. An orthogonal experiment of bionic samples was carried out, where three plane configurations were taken as factors, while the different characteristics of configuration as levels. A total of 16 bionic specimens and 1 wedge-shaped comparison specimen were constructed by SolidWorks software and then fabricated using 3D printing (polylactic acid material). A test system of soil groove was utilized to evaluate the cutting resistance of each specimen, where the soil was assumed as the foamed phenolic plastics, the cutting speed was 10 mm/s, the cutting depth was 15 mm, and the cutting time was 20 s. The explicit dynamic Finite Element (FE) software ANSYS LS-DYNA was used to simulate the cutting process of the specimen, in order to determine the relationship between the 3D geometrical toes of the foreleg claw in the mole cricket and the drag reduction performance. It was found that the cutting process of the specimen was divided into the drag increase and stable phase. Furthermore, the drag reduction performance of specimens with 3D biological geometries was significantly better than that with one- and two-dimension, as well as the wedge shape. All configurations in the three planes also presented a significant impact on drag reduction. Correspondingly, the main influencing factor of drag reduction was the cross-sectional configuration perpendicular to the growth direction of claw toes. More importantly, the cutting resistance of the specimen was reduced up to 56.96% with 3D biological geometries. The FE analysis results showed that the 3D geometrical toes of the foreleg claw in the mole cricket effectively alleviated the accumulation of soil on the tip of the specimen. As such, the soil moved smoothly along the excavation surface, thereby avoiding the accumulation of pressure on the middle and back of specimens. This process was the reason for the reduction of cutting resistance. Furthermore, an optimal configuration of soil-contacting components was also achieved to reduce the cutting resistance, while effectively improving the working efficiency of machinery without the use of external energy and auxiliary devices. Nevertheless, the actual configuration was a 3D structure of soil-contacting parts in farming and engineering machinery, where many interrelated geometric parameters were involved during optimization. Consequently, the biological geometry can widely be expected to optimize soil-contacting parts, whether to project the main configuration of bionic objects in two dimensions, or to directly transplant the 3D biological geometry with 3D reverse. The characteristic curves of 3D biological geometry were also coupled to design bionic specimens. The feasible idea can also provide an insightful promising bionic design on soil cutting parts of tillage machinery, such as openers and subsoilers. © 2021, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.